Some communication terminals have a voice communication function which enables voice communication, and a videophone function which enables videophone communication. These kind of communication terminals include a camera which captures still pictures and motion pictures, a speaker which outputs voices, a microphone which inputs voices, a LCD (liquid crystal displays) which displays pictures and others.
In case of the voice communication, a user's communication terminal acquires a voice using the microphone and transmits it to an opposite party's communication terminal as a voice signal. Further, when the user's communication terminal receives the voice signal from the opposite party's communication terminal, it outputs a voice from the speaker.
On the other hand, in case of the videophone communication, the user's communication terminal acquires a picture which is captured by a camera and transmits it to the opposite party's communication terminal as a picture signal, and at the same time, it acquires a voice using the microphone and transmits it to the opposite party's communication terminal as a voice signal. When the communication terminal receives the picture signal and the voice signal from the opposite party's communication terminal, it displays the picture corresponding to the picture signal on the LCD and also outputs the voice corresponding to the voice signal from the speaker.
In this way, the voice communication can be achieved by a voice processing at the user's communication terminals in case of the voice communication. In addition, the videophone communication can be achieved by a picture processing as well as the voice processing at the user's communication terminals in case of the videophone communication.
An example of this kind of communication terminals is a mobile phone. Japanese Patent Application Laid-Open No. 2007-228351 discloses a mobile phone equipped with a voice communication function and a videophone function. In case of the voice communication, voice signals are transmitted and received between a user's mobile phone and an opposite party's mobile phone. Moreover, in case of the videophone communication, voice signals and picture signals are transmitted and received between the user's mobile phone and the opposite party's mobile phone.
However, when the voice communication and the videophone communication are processed by the mobile phone, noises are generated inside of the mobile phone. In particular, in case of a videophone communication which needs a lot of processes inside the mobile phone, a possibility of noise generation will be increased. When the receiving level of radio wave indicated by such as RSCP (Received Signal Code Power) and RSSI (Received Signal Strength Indicator) or the like is low, quality of the voice and the picture will be declined or the communication will be disconnected occasionally due to noises generated inside the mobile phone.
Therefore, the Japanese Patent Application Laid-Open No. 2004-32804 disclosed a mobile phone which can prevent quality of the voice and the picture from deteriorating or prevent communication from disconnecting even when receiving level of the radio wave is too low to keep the sufficient communication quality. The mobile phone disclosed in Japanese Patent Application Laid-Open No. 2004-32804 switches from the videophone communication to the voice communication when sufficient quality of communication for a picture is lost while executing the videophone communication with an opposite party's mobile phone. Therefore, it can prevent the deteriorations of the voice and the picture as well as prevents the disconnections of the communication.